BACTERIOPHAGY IN A FLUID MEDIUM 47 



according to the activity of the race of bacteriophage involved, all of 

 the bacteria are dissolved, and the medium has again become hmpid. 

 Instead of selecting Shiga-Kruse bacilli, we could have prepared 

 in the same way a suspension from a bacterium of another species, 

 and combined it with a race of bacteriophage of sufficiently high activ- 

 ity against this bacterium. The final result would have been the 

 same; a complete dissolution of the bacterial cells and a clarification of 

 the medium. 



But such a complete dissolution does not take place under all con- 

 ditions; the state of the bacterium exposed to the dissolving principle 

 is of significance. Instead of taking a suspension prepared from a 

 young freshly grown culture we may inoculate the bacteriophage into 

 a fifteen-day old broth culture. A clearing of the medium, a partial 

 dissolution, results, but a certain degree of turbidity remains. Never- 

 theless, it is possible to continue to use such a medium, making as 

 many passages as may be desired. Some tube of the series when planted 

 on agar or in bouillon will remain sterile, and a drop of this tube in- 

 oculated into a suspension of young bacilli will cause a perfect dissolu- 

 tion. In the old culture, then, the bacteriophage multiplies normally, 

 although dissolution does not take place, at least, the solution is not 

 complete. What is the explanation of this reaction? To answer this 

 it is sufficient to compare the results of counting the total number of 

 bacilli existing in an old culture (this can be done by the method of 

 counting cells) with the results secured by counting the viable or- 

 ganisms only (done by the plating method). For a confirmation of 

 this type, a Shiga culture in Martin's bouillon is made, incubated for 

 14 hours, and allowed to stand at laboratory temperature for 15 days. 

 The total count of bacillary bodies will be about 625 milhons; that 

 of the viable bacilli, that is, those capable of yielding colonies when 

 transferred to agar will be about 2 milhons, in each half cubic centi- 

 meter of culture. Now, as we have seen, the bacteriophage is able 

 to develop at the expense of Hving bacteria only, these being the ones 

 which are dissolved. In the old suspension which we have mentioned, 

 in which there is only about one organism in three hundred which is 

 capable of being dissolved, it can readily be comprehended that if the 

 dissolution of a suspension be taken as a criterion, the bacteriophage 

 appears to be without action. 



As a matter of fact, it is not necessary to resort to old cultures to 

 find dead bacteria, for even in fresh bouillon cultures dead organisms 

 wiU be found after as short a time as 24 hours. In a broth culture 



